Its started turning off and on really quickly and i don't know why its doing it :S the alert on my imac that a device is being removed without it being ejected keeps coming up, this is a recent problem, not a clue why its doing it

Sounds to me that your HDD is having a problem of some sort, could be getting ready to go belly up. The notice of it ejecting off and on tells me it's shutting itself off and on... Do you have another another place to hook it up and check it out?

How long have you had it? Most WDs have a 3 year warranty, so you could go to WD support and send them a message or call them. They may tell you what to do or they'll replace it for you.

Noel

EDIT: Chris, you could try using your Mac's Disk Utility and do a Disc Repair and see what happens. It could work...